The part about your boss telling you to take it down after 2 days is what gets me. If your note was helping customers and not hurting anyone, why does it matter how long it stays up? A register is a weird place to draw a hard line about personal stuff when half the stores I walk into have signs about card minimums and no refunds taped up forever. Sounds less like a real policy and more like a control thing, and yeah, that tells you a lot about how that place runs.